(1) Field of the Invention
The present invention relates generally to rigging components used for lifting heavy objects and, more particularly, to a system for rigging components for the heads of nuclear reactor vessels.
(2) Description of the Prior Art
Nuclear reactor vessel heads must be lifted and removed periodically to perform scheduled or corrective maintenance. Also, the reactor internals may need to be lifted at the same time for similar reasons. Currently, lifting either of these components requires up to four rigging changes during a typical reactor outage. These changes are required because some reactor components must be lifted using a combination of turnbuckle pendants, solid rod lifting pendants, and/or bridge strands, while others must be lifted using latchbox pendants, solid rod lifting pendants, and/or bridge strands. The changeover between these rigging components requires a large amount of time and manpower.
It should be understood that the components being lifted are quite heavy, in some cases over 20 tons. Thus the rigging components are massive in size and require a great deal of time to change out. The time factor is important because increasing the time required to remove components increases personnel radiation exposure and the total time that a reactor must be out of service for maintenance/repair. Because the above-mentioned components are difficult to maneuver, each requirement for a rigging change increases the chance of personnel injury. Considerable cost-savings can be achieved and the chances for personnel injury may be reduced by reducing the number of rigging changes required for each lift. However, because of the capital expenditures restraints all utilities must live with, the cost of the rigging conversion must be relatively low.
Thus, there remains a need for a new and improved rigging system for nuclear reactor components that reduces the number of rigging changes required during a reactor outage while, at the same time, is easy to add to the existing rigging system.